Rupture discs have been utilized in downhole tools for some time. For example, a rupture disc may function as a safety valve when the annulus pressure reaches a predetermined value. At that pressure, the rupture disc will burst, thus causing the valve to isolate the workstring below the tool, establish communication between the annulus and the workstring above the tool, or some other desired function.
There are, however, disadvantages to conventional rupture disc designs. If the seal between the rupture disc and temporary air chamber coupled to the rupture disc is damaged, pressure may leak around the rupture disc and cause the tool to work improperly. Also, since conventional rupture discs are threaded into the tool housing using 1-1.5 threads, the rupture disc may loosen and back out of the housing before hydrostatic pressure is supplied. As a result, a gap is created between the bottom of the rupture disc and the tool housing which may also cause pressure leakage around the rupture disc.
In view of the foregoing, there is a need in the art for a rupture disc having a secondary sealing device, thus providing a more reliable rupture disc system.